This invention relates generally to the inspecting of components, and more particularly to methods and apparatus for inspecting components having non-uniform surfaces.
Eddy current (EC) inspection devices are used to detect abnormal indications in a component under test such as, but not limited to, a gas turbine engine component. At least one known EC inspection device is used to detect cracks, pings, dings, raised material, and/or other surface imperfections on a surface of the component and/or to evaluate material properties of the component including the conductivity, density, and/or degrees of heat treatment of the component.
At least one known EC device measures the interaction between an electromagnetic field generated by the EC device and the component to be inspected. For example, the EC device includes a probe coil that generates a magnetic field. When the coil/field is positioned proximate to a conductive component, an eddy current is generated on the surface of the component. A flaw on and/or near the surface of the component generates a disruption in the eddy current field which produces a secondary field that is received by the eddy current probe coil or by a sensor coil in the eddy current probe which converts the altered secondary magnetic field to an electrical signal which may be recorded on a strip chart for example.
At least one known EC device includes a relatively small coil, that is typically 0.020 inches in diameter, that is used to detect surface flaws, surface contamination, material properties, and/or a surface roughness of the component being inspected. In use, the coil is positioned normal to the surface of the component under test. A substantially constant pressure is applied to the probe as the coil is moved along the surface of the component under test to facilitate maintaining an integrity of the signal generated by the EC device. However, when the EC device is not oriented normal to the surface of the component being inspected, a “lift-off effect” may be created
When a non-continuous surface feature needs to be inspected, such as a feature on a rotating part, known differential probes may have difficulty resolving sharp curvatures, such as in chamfers, corners and/or cusps. During operation, when such differential probes encounter a chamfer, corner or cusp, the differential probe device may become skew to the surface of the component, such that a resulting lift-off effect may cause a loss of usable data. Accordingly, known EC devices may be less effective in generating an accurate response when the EC device is used to detect an abnormal condition on a component having complex geometries, and/or a component having irregular conditions such that the probe cannot consistently be placed normal to scan surface.